1. Field of the Invention
The present invention relates to a piston assembly, and more particularly to a piston assembly for a food extruder, which is airtight and operates without canting.
2. Description of Related Art
With reference to FIGS. 4 to 7, a conventional food extruder (50) in accordance with the prior art comprises a base (51), a housing (53), a drive assembly (56), a food reservoir (52) and a piston assembly (54).
The housing (53) is mounted on and protrudes up from the base (51) and has two side panels (55) and an upper bracket (57). The side panels (55) are mounted parallel to each other on the base (51), and each side panel (55) has a top end and an inside surface. The upper bracket (57) is U-shaped, is attached to the inside surfaces of the side panels (55) at the top ends.
The drive assembly (56) extends through and is attached one of the side panels (55) and has a gear assembly and a handle (561). The gear assembly is mounted rotatably in the upper bracket (57) and has multiple gears. The multiple gears include a bull gear and a pinion. The handle (561) is mounted through one of the side panels (55) and engages and rotates the bull gear when the handle (561) is turned.
The food reservoir (52) is hollow and cylindrical, is mounted between the side panels (55) below the upper bracket (57), holds food to be extruded from the food reservoir (52) and has an open upper end, a closed lower end, a chamber, an inner surface and a stuffing pipe (521). The open upper end of the food reservoir (52) faces the upper bracket (57). The closed lower end of the food reservoir (52) is near the base (51). The chamber is defined inside the food reservoir (52) to hold food. The stuffing pipe (521) allows food to be extruded from the chamber, is formed on the closed lower of the food reservoir (52) and communicates with the chamber.
The piston assembly (54) is mounted slidably through the upper bracket (57), connects to and is driven by the pinion of the gear assembly of the drive assembly, extends into or retracts from the food reservoir (52) when the handle (561) is turned and has a piston rod (541) and a piston dish (542). The piston rod (541) engages the pinion of the gear assembly of the drive assembly (56), slidably extends into or retracts from the chamber of the food reservoir (52) when the handle (561) is turned and has an upper end, a lower end and a rack. The upper end of the piston rod (541) is mounted slidably in and protrudes through the upper bracket (57). The lower end of the piston rod (541) is extends into or retracts from the chamber of food reservoir (52) when the handle (561) is turned. The rack is mounted longitudinally on the piston rod (541) between the upper and lower ends and engages the pinion.
The piston dish (542) is circular, is attached to the lower end of the piston rod (541), slides inside the food reservoir (52) and has a center, a central through hole, a fastener, an outer edge and a sealing ring (5421). The central through hole is formed through the center of the piston (542). The fastener may be a bolt, extends through the central through hole and attaches longitudinally to the lower end of the piston rod (541). The sealing ring (5421) is mounted around the outer of the piston dish (542) and presses against the inner surface of the food reservoir (52).
However, defects and shortcomings of the conventional food extruder (50) follow.
The piston dish (542) of the piston assembly (54) is attached to the lower end of the piston rod (541), and sealing ring (5421) slides against the inner surface of the food reservoir (52). When the piston dish (542) moves down and presses against food in the food reservoir (52), variations in the density and distribution of food in the food reservoir (52) applies uneven forces to the piston dish (542), which may cause the piston dish (542) to cant to an extent that the rack on the piston rod (541) disengages partially or completely from the pinion and results in partial or complete reduction of operational efficiency of the piston assembly (50) or damage to the food extruder (50).
2. When the piston dish (542) is canted in the food reservoir (52), a gap may form between the piston dish (542) and the inner surface of the food reservoir (52) such that some food in the food reservoir (52) squeezes around the piston dish (542) rather than being extruded from the stuffing pipe (521). Therefore, the conventional piston assembly (50) is not convenient in operation.
To overcome the shortcomings, the present invention provides a piston assembly for a food extruder to mitigate or obviate the aforementioned problems.